The present invention relates to a gas combustion-powered apparatus, and more specifically to a gas combustion-powered fastener-driving apparatus having a collapsible combustion volume for displacing a gas volume within a combustion chamber.
Gas combustion devices are known in the art. A practical application of this technology is found in combustion-powered fastener driving tools. One type of such tools, also known as IMPULSE brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich, U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162, 4,483,473, 4,483,474, 4,403,722, 5,197,646, and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and the engine also includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body. When a work contact element is pressed against a workpiece, a fuel-metering valve introduces a specified volume of fuel into a combustion chamber of the engine.
Upon pulling a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber, the piston and the driver blade are shot downward to impact a positioned fastener and drive it into a workpiece. The piston then returns to its original, or “ready,” position through differential gas pressures within the cylinder. Fasteners are fed magazine-style into a nosepiece, where the fasteners are held in a properly positioned orientation for receiving the impact of the driver blade. The charge of gas is a combustible fuel/air mixture, and the combustion in the chamber causes an acceleration of the piston/driver blade assembly and a resulting penetration of the fastener into the workpiece if the fastener is present in the nosepiece.
Combustion pressure in the chamber is an important consideration because such pressure affects the amount of force with which the piston may drive the fastener. Combustion pressure increases the more rapidly the fuel/air mixture within the combustion chamber can be ignited. The fuel/air mixture in the combustion chamber may be more rapidly ignited when the mixture is in a turbulent state. The ability to rapidly complete processes ancillary to this combustion operation of the tool is another important consideration. Such ancillary processes include: inserting the fuel into the combustion chamber; mixing the fuel and air within the chamber; and removing, or scavenging, combustion by-products remaining in the chamber after a combustion event.
One known method of scavenging the residual combustion by-products between combustion events is by dilution. Dilution scavenging is performed by sending fresh air flowing through the combustion chamber between combustion events to displace combustion by-products. An example of dilution scavenging is described in commonly assigned, copending application Ser. No. 10/170,736, which is incorporated by reference herein. A fan is located within the combustion chamber to create the turbulence for a more rapid, higher-energy combustion, and also to drive fresh air through the combustion chamber between combustion events. Although this process is effective to achieve rapid, high-energy combustions and scavenging, the scavenging is not always performed efficiently. Typically, a volume of air required to scavenge the combustion by-products after a combustion event is equal to approximately two and one half times the volume of the combustion chamber itself.
Another known method of scavenging, which is more efficient than the dilution method, is the displacement method. Displacement scavenging is performed by eliminating, or otherwise effectively reducing to zero, the volume within the combustion chamber itself, thereby removing all air within the volume, including that containing combustion by-products. Examples of displacement scavenging are described in patents to Cotta, U.S. Pat. No. 4,721,240, and to Gschwend, U.S. Pat. No. 5,181,495.
Cotta requires the displacement of moveable parts at the front of the combustion chamber toward a rear wall of the chamber. Displacement is thus performed by the movement of a second piston assembly through the combustion chamber in a direction opposite to the piston in the piston chamber. The second piston displaces the entire volume of gas from the combustion chamber, but does not actually reduce the volume to zero. Although reasonably efficient, the complexity of this configuration greatly increases the cost of the tool. The cost and complexity are both significantly increased by the number of extra components required for the second piston assembly, as well as a host additional electrical components (motors, batteries, control circuits, etc.) to operate the complex construction.
Gschwend displaces the combustion chamber volume by requiring that a moveable section at the rear of the combustion chamber move toward the front of the chamber to mostly collapse the chamber from behind, and reduce its volume to near zero. Force from an operator in back of the tool moves the moveable section to toward the front of the combustion chamber, thereby having the moveable section operate like Cotta's piston, but only in the reverse direction. Gschwend also separates the combustion chamber into first volume and a second combustion volume by use of a divider plate configured as a multiple-volume system, as is known in the art, to increase the energy of combustion.
To operate the tool as a multiple volume system though, Gschwend requires a complicated system of collapsing guide rods throughout the moveable section and the divider plate between the volumes. The tool's trigger also must be located at an awkward position at the rear of the tool where the operator must be positioned to push the moveable section toward the front of the tool, thereby making the tool itself cumbersome to operate. And similar to Cotta's tool as well, this tool is significantly complex, and requires a great deal of additional electrical and mechanical components to guide the opposing structures of the combustion chamber together and apart at appropriate timings.
There is a need therefore for a commercially available combustion gas fastener-driving tool having a simplified construction that reduces the need for expensive mechanical and electrical components in its construction. Such expensive components limit the availability of cordless combustion gas technology to a range of high cost applications only. A simplified single or multiple combustion volume construction, which can achieve substantially the same performance as the higher cost tools, would greatly extend the availability of combustion gas technology to more affordable, lower cost applications.